#define _CRT_SECURE_NO_WARNINGS 1
class Solution {
public:
    ListNode* merge(ListNode* l1, ListNode* l2) {
        ListNode* dummy = new ListNode(0);
        ListNode* cur = dummy;
        while (l1 != NULL && l2 != NULL) {
            if (l1->val < l2->val) {
                cur->next = l1;
                l1 = l1->next;
            }
            else {
                cur->next = l2;
                l2 = l2->next;
            }
            cur = cur->next;
        }
        cur->next = (l1 != NULL ? l1 : l2);
        return dummy->next;
    }
};